Experimental investigation of hydrogen impact on atmospheric sooting premixed methane flames
Résumé
The effect of hydrogen on aliphatic and aromatic species formation has been experimentally investigated in a methane "nucleation flame". The nucleation flame conditions were identified by laser induced incandescence (LII) at equivalent ratio Ф=1.82. The approach and the definition of the "nucleation flame " have been previously reported in our recent work [1,2]. Various stable species (C1-C6) were measured by gas chromatography while polycyclic aromatic hydrocarbons (PAHs) such as naphthalene and pyrene were measured by jet-cooled laser induced fluorescence (JCLIF). To keep the C/O ratio and temperature values constants in the sooting flame region, all H2-flames have been studied by replacing or adding the equivalent of 1.8%N2. The Pt/Rh thermocouple measurements confirmed similar temperature values in the post flame region of methane/O2/N2 and methane/H2/O2/N2flames. Moreover, additional experiments carried out in similar conditions with helium allowed to exclude the diluent affect. The new experimental results demonstrated that hydrogen can enhance significantly soot precursors (benzene, naphthalene, pyrene) even it is added at low amounts (lower than 2%). However, these aromatic compounds peak mole fraction can significantly be reduced if the experiments proceed via a low N2-amount substitution(1.8%).The soot volume mole fraction measurements and the modeling work which are in progress should confirm the importance of H atoms in the chemical growth process of PAHs and soot formation. *
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